Transparent polymer and diamond-like hydrogenated amorphous carbon thin films by PECVD technique

Abstract

Optical, electrical and structural properties of hydrogenated amorphous carbon films deposited by radio frequency plasma enhanced chemical vapour deposition technique (RF-PECVED) have been investigated thoroughly. The films were deposited using a mixture of hydrogen and acetylene gases at a low substrate temperature of 200 °C. The electrical resistivities of the films are ⩾ 109 Ω cm. The ratio of hydrogenated sp3 to sp2 bonded carbon atoms in the films is obtained by deconvoluting the infrared spectra over the 2800 cm−1–3100 cm−1 range. Polymer-like hydrogenated amorphous carbon films are grown at a low power (50 mW cm−2) having a high hydrogen content (30.3–46.1 at%). Increase in hydrogen dilution increases the total hydrogen content as well as the ratio of hydrogenated sp3 to sp2 carbon bonding and it becomes a maximum at an optimum hydrogen dilution. Similarly the grain density also increases with the increase in hydrogen dilution. On the other hand, at a higher RF power of 150 mW cm−2 much stronger C–C sp3 and C–C sp2 bonds are formed and the total hydrogen content drastically reduces to a very low value of 1.1–1.8 at%. This indicates the growth of hydrogenated diamond-like carbon (DLC) structure. The stronger C–C sp3 bonds present in the DLC film make the films harder as well as Raman active.